Method of gasifying water-containing coal

ABSTRACT

For gasifying coal, a coal-water mixture is pumped in the form of a viscous mass into a treating chamber where the mixture is heated, causing, in immediately successive steps and in said chamber, first, dehydration of the mixture by vaporizing its water content, second, gasification thereof and, third, endothermic reaction of the products precedingly obtained by the heat treatment.

United States Patent Wenzel et al.

[ Mar. 7, 1972 [54] METHOD OF GASIFYING WATER- CONTAINING COAL [72]Inventors: Werner Wenzel; Hermann Schenck, both of Aachen, Germany 1Assigneel Rheinische Braunkohlewerke A.(1.,

Cologne. Germany [22] Filed: Aug. 22, 1969 211 Appl. No.: 852,430

[30] Foreign Application Priority Data Aug. 22, 1968 Germany ..P 17 96050.8

52] u.s.c1 ...48/202,48/92,48/99 [51] lnt.Cl ..Cl0j3/00,C10j3/46 [5s]FieldofSearch ..48/73,99,92,202,206,210, 48/197, 226, DIG. 7; 23/284,260, 262, 212 B, 212,

[56] References Cited UNITED STATES PATENTS Royerson et al ..48/2022,485,875 10/1949 Gorin et al. ..48/206 X 2,659,668 11/1953 Mayland2,768,935 10/1956 Watkins... 1,392,788 10/1921 Paris, Jr... 1,592,8607/1926 Leonarz 1,592,861 7/1926 Leonarz 3,533,739 10/1970 Pelczarski etal. ..48/92 X FOREIGN PATENTS OR APPLICATIONS 465,548 5/1937 GreatBritain ..48/92 Primary Examiner-Joseph Scovronek Attorney-Edwin E.Greigg [57] ABSTRACT For gasifying coal, a coal-water mixture is pumpedin the form of a viscous mass into a treating chamber where the mixtureis heated, causing, in immediately successive steps and in said chamber,first, dehydration of the mixture by vaporizing its water content,second, gasification thereof and, third, endothermic reaction of theproducts precedingly obtained by the heat treatment.

9 Claims, 2 Drawing Figures METHOD OF GASIFYING WATER-CONTAINING COALBACKGROUND OF THE INVENTION This invention relates to a method of andapparatus for gasifying water-containing coal or the like.

Coals used for obtaining combustible gases often have a very high watercontent. Thus, brown coal at the time of its recovery from deposits maycontain 50-60 percent of water. Other coals may be dry in theirdeposits, but are recovered from open pits by a flushing processresulting in a coal-water mixture of 40-50 percent water.

In order to gasify coal having such substantial water content, thecoal-water mixture has heretofore been first subjected to a separatedrying step for dehydrating the wet coal by separating the watertherefrom. Thereupon, the dry coal has been introduced into a reactionchamber for heat treatment under elevated temperatures resulting in thegeneration of combustible gases and coal residue.

OBJECTS AND SUMMARY OF THE INVENTION It is an object of the invention toprovide an improved method and apparatus for practicing the same topermit a simple and economical gasifying of water-containing coalwithout the necessity of subjecting the coal-water mixture to a separateprior drying or water-separating step.

It is a further object of the invention to provide an improved methodand apparatus for practicing the same to utilize directly the watervapors, obtained during the dehydration of the coal, in aiding theendothermic reaction following gasification of the dried coal.

Briefly stated, according to the invention the coal-water mixture isintroduced into a reaction chamber as a viscous or fluid mass. In thereaction chamber the mixture first loses its water content byvaporization and then the vapor is reduced directly with the solidgasifiable coal components while a combustible gas is generated. Thus,the water of the coal-water mixture itself is utilized in the gastifyingprocess.

The invention will be better understood, as well as further objects andadvantages will become more apparent, from the ensuing detailedspecification of two exemplary embodiments taken in conjunction with thedrawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic side elevationalview of a first embodiment of the apparatus according to the invention;and

FIG. 2 is a schematic side elevational view of a second embodiment ofthe apparatus according to the invention.

DESCRIPTION OF THE FIRST EMBODIMENT Turning now to FIG. 1, theembodiment illustrated therein is particularly adapted for the treatmentof a mixture of brown coal and approximately 60 percent of water. Thismixture is introduced into the apparatus through a hopper 13.Immediately adjacent the outlet of hopper 13 there is disposed a pistonpump generally indicated at 11 having a reciprocating piston 12.Downstream of the hopper 13 there is disposed a check valve assemblygenerally indicated at 14 having a housing 14a, a reciprocable ball 15,a spring 16, a spring seat disc 17 and a valve seat 14b formed in thevalve housing 14a. The spring 16 urges the ball against the valve seat14b in opposition to the feeding force exerted to the coal-water mixture30 by the pump 11. Thus, during operation of the latter, pressurestrokes of piston 12 cause a downstream displacement of ball 15 so thatthe mixture 30 may pass through the valve opening contoured by valveseat 14b, whereas during return strokes of piston 12, the ball 15, byvirtue of spring 16, is in its seat preventing backflow and maintainingpressure of the mixture downstream of valve assembly 14.

A valve 14 is joined in the downstream direction by a connecting conduit18 which continues in one or several reaction tubes 20 (only one shown)surrounded by a jacket or heating chamber 19. The latter has an inlet 22for admitting, and an outlet 23 for discharging, a heating medium. Theheating chamber 19 is joined by a separating chamber 25 by means of aconduit 24. The separating chamber 25 has at its upper end a gasdischarge outlet 26 provided with a control valve 27. At the lower endof the separating chamber 25 there is disposed, for the discharge ofsolid, nongasifiable products, an outlet 28 controlled by a pair ofsliding gates 29.

THE METHOD PRACTICED BY THE FIRST EMBODIMENT In operation, thewater-coal mixture 30 is introduced into the apparatus shown in FIG. 1through the hopper 13. By means of reciprocating piston 12, the mixtureis urged as a viscous mass against the ball 15 of the check valve 14. Asthe ball 15 yields and is unseated downstream, the mass is advancedthrough check valve 14 and the connecting conduit 18 and is introducedas mixture 31 into the reaction tube 20. Through the inlet 22 there isintroduced into the heating chamber 19 a fluid heating medium which, forexample, may be high-temperature helium taken from the cooling system ofa nuclear reactor. It is also feasible to use a part of the obtainedcombustion gases for furnishing the necessary heat, Subsequent to theheat exchange in chamber 19, medium is discharged therefrom through theoutlet 23. By virtue of heating the reaction tube 20, the mixture 31forced thereinto is first dried to obtain a mass of dry coal 32.Thereafter, the dry coal is gasified and reacted upon in the reactiontube 20. The products of the reaction, i.e., gas 34 and the residue 33which is mostly coal ash-are introduced into the separating chamber 25through the connecting conduit 24. The gas 34 is taken out from thechamber 25 through the outlet 26 in a rate determined by control valve27. The residue 33 accumulating at the bottom of the separating chamber25 is discharged through outlet 28 by alternately opening and closingthe dual sliding gate 29.

DESCRIPTION OF THE SECOND EMBODIMENT Turning now to the apparatus shownin FIG. 2, the coal water mixture 42 is fed through a hopper 41 andforced through a conduit 44 by a rotary pressure pump 40 having a worm43. It is seen that in this embodiment the feeding means does notcontain a valve assembly (such as valve assembly 14 in the firstembodiment): a backflow of material is nevertheless prevented by anappropriate design of the cross section and length of conduit 44 forgenerating a sufficient frictional resistance.

The conduit 44 ends, with an extension 53, in a treating chamber 45where both the gasification and separation take place as hereinafterdescribed.

At the upper lateral portion of the chamber 45 there is provided anoutlet 46 through which the residue is admitted into a collecting tank47. The latter is at its lower end providing with a sliding gate 48which, similarly to the gate 29 of FIG. 1, may be designed as a dualgate. The residue may be discharged from the tank 47 upon operation ofthe gate 48.

At the upper terminus of the reaction chamber 45 there is provided a gasdischarge nipple 49 containing a control valve 40 for permitting ametered removal of the gas obtained from the coal during the reactionprocess.

The heat necessary for raising the temperature of the coalwater mixturefor the purpose of vaporizing the water, for decomposing the coal andfor performing an endothermic reaction, may contact the mixture directlyor indirectly. It is noted that in the first embodiment (FIG. 1) suchheat treatment of the coal is indirect inasmuch as the heating mediumcirculated through jacket 21 does not directly contact the material tobe treated. In the apparatus according to the second embodiment (FIG.2), however, the heat exchange takes place in chamber 45 by virtue of adirect contact between the heating medium and coal-water mixtureintroduced into chamber 45 through conduit 44. For effecting theaforenoted direct contact, at the base of the chamber 45 and in thesidewall thereof there are provided, respectively, ports 51 and 55associated with respective control valves 52 and 56. Through theseports-one serving as an inlet and the other as an outleta heatingmedium, such as molten metal, preferably molten lead, may be circulated.

THE METHODS PRACTICED BY THE SECOND EMBODIMENT According to a firstmethod of practicing the invention by means of the apparatus shown inFIG. 2, the heating medium (molten metal, such as liquid lead)circulates through the chamber 45 in an upward direction. Thus, port 51serves as an inlet, while port 55 serves as an outlet for the moltenlead. Since the material 44 introduced into chamber 45 at the lowerportion thereof also proceeds upwardly, the flow of material 44 and thatof the heating medium, i.e., the molten lead, are codirectional. Thetemperature of the molten lead is, e.g., I000 C. upon introductionthrough port 51 and is cooled to, e.g., 750 C. after heat exchange andupon discharge through port 55. The level of the molten lead bath 57 isindicated at 54. Externally of the treating chamber 45 the temperatureof the lead is again increased (for example, by means of heat taken froma nuclear reactor) and the lead may be submitted to a purifying processduring which, for example, sulphur may be used.

The coal-water mixture introduced into the lead bath 57 through theextension 53 is promptly dried and gasified, whereby the separated gasescause in the lead bath a strong turbulence of the coal and the productsof gasification. Hereby an intensive reaction takes place between thewater vapor, the carbon dioxide (obtained from the degasification) andthe carbon, while permanent combustible gases are generated. These gases58 accumulate in the upper portion of the reaction chamber 45 above thelead bath 57 and are discharged through the outlet 49. The residue59mostly coal ashsettles on the .top of the lead bath 57 and flows overto tank 47 from which it is discharged upon operation of gate 48.

A second method of practicing the invention by means of the apparatusshown in FIG. 2 will now be described.

In process including a counterflow-type heat exchange, it has beenassumed heretofore that, from both technical and economical points ofview, the best results could be obtained when the heat exchange wasperformed indirectly through separating walls. Stated in differentterms, the medium carrying the heat, on the one hand,,and the materialor material mixture to be heated, on the other hand, do not enter intodirect contact with one another. A counterflow-type heat exchange withno direct contact may be effected by means of the apparatus of FIG. 1.

If a heat exchange by direct contact between the two material flows isto be effected, a counterflow process in general has not been deemedpossible because the fluid medium which is used as heat carrier oftencarries away material particles from the opposite flow unless the lattermeets certain conditions with respect to particle weight and volume. Incase of coal-water mixtures of the type with which this invention isconcerned, such conditions are not met. For this reason, raw brown coal,which is particularly adapted for use in the present invention, has beenheretofore directly contacted with hot gases only by means of concurrentflow process.

Contrary to expectations based on processes performed ac- I cording tothe prior art, it has been found that in case a molten metal, preferablyliquid lead, was used as a heat-carrying medium, the transfer of heat bydirect contact to the mixture could be performed in a counterflowprocess without experiencing the aforenoted difficulties.

According to a second method of practicing the invention by means of anapparatus shown in FIG. 2, a direct contact heat exchange by counterflowis effected. For this purpose, the molten lead passes through thechamber 45 downwardly, that is, in a direction opposing the upward flowof the coal mixture introduced into the lower portion of chamber 45 fromconduit 44. To effect a downward flow of the lead bath 57, the moltenlead is introduced into chamber 45 through port 55 and discharged fromchamber 45 through port 51. It was found, as noted hereinabove, that themolten lead did not carry with it particles from the opposed flow. Thisdisadvantage being absent, the process may fully benefit from a dualadvantage of the counterflow contact. In the first place, the heatexchange is more efficient than in the case of a contact betweencoinciding flows: It has been found that the molten lead, which upon itsentering the treating chamber 45 through port 55 had a temperature of1000 C. cooled to about 450 C. upon its discharge through port 51. Inthe second place, the different temperatures along the flow path of themolten lead are best suited for the optimal temperature requirementsduring the successive different heat treatments to which the upwardlyflowing coal material is exposed at different heights. Thus, followingthe introduction of the coalwater mixture 44 into the lower portion oftreating chamber 45, the first step is to withdraw the water from themixture. This is effected by vaporizing the water. The temperatures forthis step may be relatively low: The temperatures of 450-650 C. of thelead bath in this part of the chamber (close to discharge port 51) arewell suited for this purpose. As the dehydrated coal proceeds upwardly,it is submitted to a gasification step. In this region of the lead bath57 the prevailing temperatures are 650-750 C. Finally, adjacent theupper level 54 of the lead bath an endothermic reaction takes placewhich requires the high temperatures of approximately 750- 1,000 C.prevailing in the upper part of the lead bath.

In all other aspects the precedingly described method is identical tothe method in which direct contact between codirectional flows takesplace, identified hereinabove as the first method for practicing theinvention by means of an apparatus shown in FIG. 2.

As set forth in the foregoing description relating to both embodimentsaccording to FIGS. 1 and 2, the dehydration of the coal is carried outimmediately preceding the gasification and successive endothermicreaction and all the water vapors obtained as a result of saiddehydrating step participate in the endothermic reaction and form partof the equilibrium thereof. It may be consequently stated that at givengasifying temperature and pressure, the amount of water vaporsdetermines substantially the composition of the obtained gas which maybe, for example, a mixture of two or more of the following gases invarying proportions: hydrogen, carbon monoxide, carbon dioxide andmethane.

The quantity of generated water vapors, in turn, is determined by thewater content of the coal-water mixture. The pumpability of thismixture, as well as the frictional resistances opposing the flow of themixture through the conduits to the treating chambers are functions ofthe mixture consistency which, again, is determined by its watercontent. It was found, for example, that a mixture of brown coal andwater may be pumpable when the water content is upward of approximately20 percent.

It follows from the foregoing that different types of pumps may beselected to advance mixtures of different consistency.

If necessary, the aforenoted frictional forces may be reduced by addingoil or other lubricant to the coal-water mixture, particularly tomarginal regions that are close to or in contact with the walls ofconduits. It is advantageous to add such lubricants only to the marginalzones of the coal-water mixture for keeping the required quantities ofsuch lubricants small. Thus, the lubricants may be introduced into theadvancing mixture through orifices in the conduit wall.

The determination of temperature, pressure and water vapor conditionsfor obtaining a predetermined composition of the final gas product iswell known from the thermodynamics of this process. Thus, by selectingthe proper temperature and pressure conditions and, in particular, byusing a coal with a determined initial water content, gases for thereduction of iron ore, gases for various gas syntheses, or high-caloriegases for heating purposes may be obtained.

That which is claimed is:

l. A method of gasifying solid fuel with high water content, comprisingthe following steps:

A. circulating molten lead as a heat-carrying medium through a treatingchamber,

B. forming a bath of sad circulating molten lead in said treatingchamber, C. heating said molten lead externally of said treatingchamber, D. introducing a coal-water mixture into the molten lead bath,E. effecting in said molten lead bath as a result of direct contact l. adehydration of said mixture by vaporizing its water content and 2. animmediately successive gasification of the dehydrated coal and F.discharging from said treating chamber the gases and the solid residuesobtained as a result of step (E). 2. A method as defined in claim 1,wherein said mixture is introduced into said bath in a viscouscondition.

3. A method as definedin claim 1, wherein said mixture is introducedinto said bath in a fluid condition.

4. A method as defined in claim 1, wherein said molten metal and saidmixture are in a codirectional flow in said chamber.

5. A method as defined in claim 1, wherein said molten lead and saidmixture are in a counterflow in said chamber.

6. A method as defined in claim 1, wherein said mixture is introducedinto said chamber through a tubular conduit; a lubricant is added tosaid mixture prior to step (D) for reducing the frictional resistanceencountered in said tubular conduit.

7. A method as defined in claim 1, wherein said solid residuesaccumulate on the top of said bath and are discharged therefrom.

8. A method as defined in claim 5, wherein the temperature of saidmolten lead bath in said chamber increases in the direction of flowofsaid mixture.

9. A method as defined in claim 1, wherein step (E)(2) includes anextraction of gases from said dehydrated coal and an immediatelysuccessive endothermic reaction of said gases with the water vaporsobtained as a result of step (E)( l

2. an immediately successive gasification of the dehydrated coal and F.discharging from said treating chamber the gases and the solid residuesobtained as a result of step (E).
 2. A method as defined in claim 1,wherein said mixture is introduced into said bath in a viscouscondition.
 3. A method as defined in claim 1, wherein said mixture isintroduced into said bath in a fluid condition.
 4. A method as definedin claim 1, wherein said molten metal and said mixture are in acodirectional flow in said chamber.
 5. A method as defined in claim 1,wherein said molten lead and said mixture are in a counterflow in saidchamber.
 6. A method as defined in claim 1, wherein said mixture isintroduced into said chamber through a tubular conduit; a lubricant isadded to said mixture prior to step (D) for reducing the frictionalresistance encountered in said tubular conduit.
 7. A method as definedin claim 1, wherein said solid residues accumulate on the top of saidbath and are discharged therefrom.
 8. A method as defined in claim 5,wherein the temperature of said molten lead bath in said chamberincreases in the direction of flow of said mixture.
 9. A method asdefined in claim 1, wherein step (E)(2) includes an extraction of gasesfrom said dehydrated coal and an immediately successive endothermicreaction of said gases with the water vapors obtained as a result ofstep (E)(1).